Guide bar for chain saws



June 10, 1 N. c. BYE

GUIDE BAR FOR CHAIN SAWS Filed Jan. 5, i948 Patented June 10, 1952 GUIDEBAR FOR CHAIN SAWS Norman 0. Bye, Wyndmoor, Pa.,

Henry Disston and Sons, Inc.,

assignor to Philadelphia, Pa.,

a corporation of Pennsylvania Application January 5, 1948, Serial No.595

2 Claims. (Cl. 143-32l This invention relates to chain saws and moreparticularly to improvements in the guide rails which, in saws ofconventional type, afford backing support for the cutting chain.

A primary object of the invention is to provide a guide rail which, byreason of an asymmetrical form hereinafter described, provides theproper supporting contact between the guide rail and the travellingchain, with uniform minimum pressure at all points, thereby materiallyimproving the operating characteristics of the saw.

An object of this invention is to reduce vibration caused by periodiccontact which occurs between a travelling chain and a symmetrical guiderail.

Another object is to reduce excessive wear at the localized pressurepoints which are built up between the travelling chain and a symmetricalguide rail.

A still further object is, through a more complete supporting of thechain, to lessen its tendency to chatter or bounce when cutting.

In the attached drawings:

Fig. 1 is a diagrammatic view showing a portion of a guide rail made inaccordance with the invention and indicating also the chain andchaindriving sprocket in operative association with said rail; and

Figs. 2 and 3 are diagrammatic views illustrating the principle of theinvention.

With reference to Fig. 1 or the drawings, reference numeral l indicatesthe fragmentary part of a guide rail with which the present invention isprimarily concerned; reference numeral 2 indicates a chain-drivingsprocket, said rail and sprocket being shown in the relative positionswhich they normally assume in conventional chain saw assembly. A cuttingchain 3, indicated in broken lines, is trained about the sprocket 2 andis guided at the edges of the rail l as illustrated.

In accordance with the invention, the guide rail l departs fromconventional symmetrical form to the extent that the portion of the railwhich adjoins the sprocket 2 at one side is shaped so that the chain atthat side of the sprocket may assume a concave contour, as indicated at4, while the portion of the rail adjoining the opposite side of thesprocket exhibits a generally convex edge contour, as indicated at 5,merging smoothly into the sprocket periphery as illustrated. Inoperation, the sprocket will rotate in the direction indicated by thearrow, so that the provision for the concave contour of the chain is atthe side on which the chain leaves the sprocket while the convex portion5 is at the side from which the chain approaches the sprocket. The chainsupporting edge 8 of the rail to which the chain passes from thesprocket is smoothly contoured and in the present instance is oflongitudinally convex form similar to the edge 5. Unlike the latteredge, however, the terminal end portion of the edge 8 which adjoins thesprocket follows a line which if extended beyond the end of the saidedge would intersect the peripheral portion of the sprocket, the saidterminal end portion of the edge 8 thus forming an inset angular recesswith an imaginary line 3 intersecting the terminal end of said edge andlying tangent to the sprocket. It is this angular recess which permitsthe chain to assume the concave contour at 4 described above.

The functional characteristics of this construction are best illustratedby reference to Figs. 2 and 3. In each of these figures, the referencenumeral 6 indicates a sprocket and the reference numeral 1 a chaintrained about the sprocket. In Fig. 2 the sprocket i stationary and thechain in suspension assumes a substantially symmetrical contour withrespect to a vertical line intersecting the rotary axis of the sprocket.In Fig. 3 the sprocket 6 is assumed to be rotating in the direction ofthe arrow and in this case, the chain 1 assumes an asymmetrical contourexhibiting a concavity on that side of the sprocket from which the chainpasses; and a convexity of lesser order at the opposite side. Thisasymmetrical contour is a factor jointly of the rotation movement of thesprocket and the friction which, while small, is present in the pintlepins of the articulated chain. Departure of the chain from its normalsymmetrical contour is characteristic but the extent thereof will varywith the speed cf rotation of the sprocket.

Within a given limited speed range, it is possible to determine the meanpath of travel of the chain.

It is evident that if a guide rail of the general character shown inFig. 1 is shaped so that the chain-guiding edge thereof conforms to thesymmetrical pattern of the chain shown in Fig. 2, then when the sprocketis in operation, the chain, by reason of its tendency to depart from thesaid symmetrical pattern in accordance with the principle illustrated inFig. 3, will exert a positive pressure upon that part of the rail whichimmediately adjoins the one side of the sprocket, and will tend to leavethe rail in that part which immediately adjoins the opposite side of thesprocket. This lack of conformity between the guide rail and the normalasymmetrical path of travel of the chain, gives rise to a number ofundesirable functional effects such as the development of areas of highpressure between the rail and the chain, with resultant undue wear inboth elements, impact of the chain against the rail with resultantavoidable vibration, and lack of adequate support for the chain attending to cause chattering or bouncing of the chain during cuttingoperations/ All of these undesirable characteristics are avoided bypractice of the present invention. In accordance with the latter, theguide rail is shaped, preferably to conform to the mean asymmetricalpattern of the chain within the relatively narrow speed limits of normaloperation. The guide rail shown in Fig. l is so designed, and the mannerin which it functions in the avoidance of the undesirablecharacteristics mentioned above will be obvious. Since the guide railconforms approximately to the normal path of travel of the chain, thelatter will tend to track smoothly on the rail without impact. Thusvibration is reduced to a minimum, high pressure areas are eliminated togive uniformly distributed wear, and full support is given to the chainat all points, resulting in smooth and easy cutting.

It will be understood that the principle of the invention may finduseful application in chain saws employing guide rails of other overallshape than that illustrated in the drawings and that in this respectthere is no implied limitation excent as imposed by the terms of thefollowing claims.

I claim:

1. In a chain saw, a cutting chain, a chaindriving sprocket, and achain-supporting rail affording support for the chain at both sides ofthe sprocket, the chain supporting edges of the rail being generally oflongitudinally convex contours and directing the chain tangentially tothe sprocket on the one side and at the other side of the sprocket beingsmoothly contoured and extending into proximity to the periphery of thesprocket, the sprocket-adjoining end of said smoothly contoured edgebeing angularly disposed with respect to a line intersecting theterminal end of said edge and tangent to the sprocket and defining aninset angular recess between the said edge and the peripheral edge ofthe sprocket into which recess the chain may diverge in transition fromthe sprocket to the said rail edge.

2. In a chain saw, a cutting chain, a chaindriving sprocket, and achain-supporting rail affording support for the chain on both sides ofthe sprocket, said rail directing the chain tangentially to the sprocketon the one side and at the other side of the sprocket being generally oflongitudinally convex and smoothly contoured form and extending intoproximity to the periphery of the sprocket, the sprocketadjoining end ofsaid smoothly contoured edge being angularly disposed with respect to aline intersecting the terminal end of said edge and tangent to thesprocket and defining an inset angular recess between the said edge andthe peripheral edge of the sprocket into which recess the chain maydiverge in transition from the sprocket to the said rail edge.

NORMAN C.

Country Date Great Britain July 21, 1927 Number

